Self-inactivation of HIV by its own RT/RNase H
K. Moelling, A. Matskevich, L. Elzaouk, S. Mathur, J. Heinrich, J.-S. Jung, and T. Kwok
Institute of Medical Virology, University of Zurich, Switzerland
Corresponding author: moelling@immv.unizh.ch
The Ribonuclease H (RNase H) of HIV is an essential enzyme for retroviral replication. It is
specific for cleavage of RNA in RNA-DNA hybrids and required for removal of the viral
RNA genome during DNA synthesis. Together with the Reverse Transcriptase (RT) it is a
polyprotein which forms a dimer. It is the only retroviral enzyme not yet targeted for
antiretroviral therapy. The RNase H is structurally highly conserved in many species and
plays a general role in removal of RNA primers required for DNA synthesis or replication.
Two cellular RNases H are known H1 and H2ABC whereby deficiency of RNase H2A leads
to mental retardation.
We are targeting the RNase H of HIV not by an inhibitor but an activating
oligodeoxynucleotide, which generates an RNA-DNA hybrid. This induces the RT/RNase H
to cleave its own RNA before it is copied and therefore inactivate itself. We designed a
partially double-stranded 54mer oligodeoxynucleotide (ODN) targeted to the highly
conserved polypurine tract PPT, the site for initiation of second strand DNA synthesis.
Treatment of HIV-infected cells inhibit HIV infection with laboratory strains as well as HIV
patient isolates, including multi-drug-resistant strains (1,2). The ODN destroys HIV RNA
efficiently inside the cell before DNA provirus formation (1). The effect is highly sequencespecific as tested by different HIV variants. Furthermore the RNA from another virus strain,
containing three mismatches in the PPT, is only weakly affected (3). Treatment of cell-free
HIV particles in vitro abrogates their infectivity (4). This is explained by the fact that the
RT/RNase H is virion-associated. Furthermore we established a mouse model for a retrovirus
with some HIV-like properties. We used the oncogenic Spleen Focus Forming Virus SFFV.
Intravenous treatment of mice chronically infected with the SFFV, reduces the virus load in
blood transiently or long-lasting, depending on the regimen of therapy. Early treatment of
mice can reduce disease progression or even completely prevent infection (5).
The antiviral effect depends on the complementarity of the ODN to the target RNA and on the
sequence of the second strand (3,4). The ODN forms an RNA-DNA hybrid and activates the
viral RT/RNase H prematurely, which irreversibly destroys the viral RNA before a DNA copy
is made (3,4). No such hybrid is formed with cellular RNA. The ODN may be designated as
siDNA, since it resembles siRNA in respect to length, sequence specificity and the enzyme
involved: RNase H and PIWI, which are related during evolution in structure and function (6).
In summary, this novel anti-HIV suicide mechanism is based on the premature activation of
its RNase H. It may be applicable to prevent HIV infection during sexual transmission as
microbicide, since it is active against virus particles. It may also be useful as prevention of
mother-to-child transmission by reduction of the viral load in the blood of infected mothers or
as post-exposure prophylaxis or as therapeutic of patients with multi-drug resistant viruses.
(1,2) Jendis et al., AIDS Res.Hum.Retroviruses (1996, 98); (3) Moelling et al., FEBS Letters
(2006); (4) Matskevich et al., AIDS Res.Hum.Retroviruses (2006); (5) Matzen et al., Nature
Biotech (2007); (6) Moelling et al., CSH Symp. 71 (2006).